Fragments of plastic have been found in every single species of turtle in a new study spanning the world's oceans.

Microplastic particles and tiny fibres were found in the guts of more than 100 turtle carcasses from the Atlantic, Pacific and Mediterranean.

A large proportion of the material extracted came in the form of fibres like those used in clothing, cigarette filters and fishing nets, but the scientists also found microbeads of the kind used in cosmetics.

The team was searching for synthetic particles less than 5mm in length, and found a total of 800 distributed among every turtle they studied, representing all seven species of these marine reptiles.

But since only part of each animal's gut was studied, the true number ingested could be 20 times higher, according to the researchers.

Likely sources of the particles are thought to be polluted seawater and sediments, or consumption of contaminated prey and plants.

"The effect of these particles on turtles is unknown," said Dr Emily Duncan from the University of Exeter, who led the study.

"Their small size means they can pass through the gut without causing a blockage, as is frequently reported with larger plastic fragments.

"However, future work should focus on whether microplastics may be affecting aquatic organisms more subtly.

"For example, they may possibly carry contaminants, bacteria or viruses, or they may affect the turtle at a cellular or sub-cellular level. This requires further investigation."

The findings were published in the journal Global Change Biology.

Senior author Professor Brendan Godley, also from the University of Exeter, said: "It really is a great shame that many or even all of the world's sea turtles have now ingested microplastics.

"At the moment, this is not the main threat to this species group but it is a clear sign that we need to act to better govern global waste."

The worst affected turtles were from the Mediterranean, the study found.

The Exeter team worked in collaboration with Greenpeace scientists.

Louise Edge, plastics campaigner at the environmental group, said: "This important research demonstrates the breadth of our plastics pollution problem.

"Our society's addiction to throwaway plastic is fuelling a global environmental crisis that must be tackled at source."

Turtles were some of the earliest ocean animals documented eating plastics, with scientists reporting bags being found in their stomachs as early as the 1980s.

Another recent study found that baby turtles may be particularly vulnerable to this pollution, with around half of very recent hatchlings already having stomachs full of plastic.

Besides eating plastic, scientists have reported the marine reptiles dying after becoming tangled in debris ranging from beer can holders to fishing nets.